1. Field of Use
This invention relates generally to movable window units for the roof of a crane operator's cab.
2. Description of the Prior Art
In some mobile truck cranes wherein a rotatable crane upper is mounted on a carrier, the crane upper includes a crane operator's cab which has windows on all sides thereof, including the roof, to provide the crane operator with maximum visibility and enable him to see the surrounding environment, the load being handled by the crane, and the crane boom. In some prior art cranes, the window in the cab roof is fixedly mounted in an opening in the cab roof and a defroster and windshield wiper are provided to keep the roof window clear so that the operator can see the boom therethrough. Also, the window creates distortion and is not too acceptable when maximum visibility is desired. In other cranes, the roof window can be moved between open and closed positions since many crane operators prefer to be able to view the boom and the machinery and cable at the end of the boom directly, thereby ensuring greater certainty and safety in crane operations. Since, on hydraulic machines, booms are typically hinged behind the operator and boom angles are 80.degree. from horizontal, a directly overhead view without window obstruction is required.